1. Field of the Invention
This invention relates to centrifugal braking devices, and more particularly to a centrifugal braking device adapted to be actuated to stop the rotation of a shaft to be braked when the rotational speed of the latter reaches a predetermined level.
2. Description of the Prior Art
A centrifugal brake adapted to be actuated to apply the brake to a shaft to be braked when the rotational speed thereof reaches a predetermined level has generally been well known as a safety brake. Such centrifugal brake is of a construction such that centrifugally activated members mounted on the shaft to be braked project outwardly into contact with a braking surface so as to apply the brake to the shaft to be braked by the friction created between them. Thus this well-known safety brake is capable of preventing an increase in the rotational speed of the shaft to be braked over and above a predetermined level but is not capable of stopping the rotation thereof. Proposals have hitherto been made to provide the braking surface with offset portions for receiving the centrifugally activated members when the latter project outwardly to lock the shaft to be braked and stop the rotation thereof. However, since the shaft to be braked is instantaneously locked, component parts of this brake must have strength high enough to withstand an impact of a high magnitude produced when the shaft to be braked is locked. One problem encountered with this type of braking device is that, when the braking device is used with a hoist, etc., and the braking device has been actuated, it is impossible to unlock the braked shaft unless the load suspended by the hoist is removed by a separate device.